1. Field of the Invention
The present invention relates to an engine included in a saddle type vehicle such as a motorcycle, a tricycle or other vehicle, and more particularly, the present invention relates to an engine having a balancer shaft.
2. Description of the Related Art
A conventional engine included in a saddle type vehicle or the like has a crank shaft, and a piston is connected to the crank shaft via a connecting rod. When the piston moves up and down within a cylinder, the crank shaft is rotated via the connecting rod.
A balancer shaft and a main shaft engaging with the crank shaft are disposed in the vicinity of the crank shaft.
The balancer shaft has a balancer gear and a balancer weight. The balancer shaft is rotatably supported by a pair of bearings provided on a crank case.
The balancer gear engages with a crank gear of the crank shaft. The balancer gear has the same diameter as that of the crank gear.
The crank shaft and the main shaft are connected with each other via a clutch mechanism such that a driving force provided by the crank shaft is transmitted to the main shaft through the clutch mechanism.
The main shaft has a plurality of shift gears. A gear is arbitrarily selected from the plurality of shift gears and brought into engagement with a gear of a drive shaft, thereby providing variable speed control. See, for example, JP-B-06-89813.
In the conventional engine of this type, however, the respective centers of gravity of the crank shaft, balancer shaft and cylinder are spaced away from one another. It is thus impossible to centralize the mass.